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Sökning: WFRF:(Tarvainen L)

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  • Dai, L. L., et al. (författare)
  • Reduced photosynthetic thermal acclimation capacity under elevated ozone in poplar (Populus tremula) saplings
  • 2021
  • Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 27:10, s. 2159-2173
  • Tidskriftsartikel (refereegranskat)abstract
    • The sensitivity of photosynthesis to temperature has been identified as a key uncertainty for projecting the magnitude of the terrestrial carbon cycle response to future climate change. Although thermal acclimation of photosynthesis under rising temperature has been reported in many tree species, whether tropospheric ozone (O-3) affects the acclimation capacity remains unknown. In this study, temperature responses of photosynthesis (light-saturated rate of photosynthesis (A(sat)), maximum rates of RuBP carboxylation (V-cmax), and electron transport (J(max)) and dark respiration (R-dark) of Populus tremula exposed to ambient O-3 (AO(3), maximum of 30 ppb) or elevated O-3 (EO3, maximum of 110 ppb) and ambient or elevated temperature (ambient +5 degrees C) were investigated in solardomes. We found that the optimum temperature of A(sat) (T-optA) significantly increased in response to warming. However, the thermal acclimation capacity was reduced by O-3 exposure, as indicated by decreased T-optA, and temperature optima of V-cmax (T-optV) and J(max) (T-optJ) under EO3. Changes in both stomatal conductance (g(s)) and photosynthetic capacity (V-cmax and J(max)) contributed to the shift of T-optA by warming and EO3. Neither R-dark measured at 25 degrees C (Rdark25) nor the temperature response of R-dark was affected by warming, EO3, or their combination. The responses of A(sat), V-cmax, and J(max) to warming and EO3 were closely correlated with changes in leaf nitrogen (N) content and N use efficiency. Overall, warming stimulated growth (leaf biomass and tree height), whereas EO3 reduced growth (leaf and woody biomass). The findings indicate that thermal acclimation of A(sat) may be overestimated if the impact of O-3 pollution is not taken into account.
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3.
  • Ciavola, G., et al. (författare)
  • Status report of the MS-ECRIS construction
  • 2007
  • Ingår i: High Energy Physics & Nuclear Physics - Chinese Edition. - 0254-3052. ; 31, s. 13-17
  • Tidskriftsartikel (refereegranskat)abstract
    • The design of each component of the Multipurpose Superconducting ECR Ion Source (MS-ECRIS) has been completed and some items are ready. The magnets and the cryostat are under construction at ACCEL and the commissioning is scheduled for March 2007. The mechanical have been optimized and their construction is under way, the microwave system is under refurbishment and the 65kV power supply is available and upgraded for afterglow operations. Pumping and extraction system were adapted to the EIS testbench of GSI Darmstadt. The description of,each part will be given in the paper along with a schedule of the forthcoming development and experiments.
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4.
  • Smith, N. G., et al. (författare)
  • Global photosynthetic capacity is optimized to the environment
  • 2019
  • Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 22:3, s. 506-517
  • Tidskriftsartikel (refereegranskat)abstract
    • Earth system models (ESMs) use photosynthetic capacity, indexed by the maximum Rubisco carboxylation rate (V-cmax), to simulate carbon assimilation and typically rely on empirical estimates, including an assumed dependence on leaf nitrogen determined from soil fertility. In contrast, new theory, based on biochemical coordination and co-optimization of carboxylation and water costs for photosynthesis, suggests that optimal V-cmax can be predicted from climate alone, irrespective of soil fertility. Here, we develop this theory and find it captures 64% of observed variability in a global, field-measured V-cmax dataset for C-3 plants. Soil fertility indices explained substantially less variation (32%). These results indicate that environmentally regulated biophysical constraints and light availability are the first-order drivers of global photosynthetic capacity. Through acclimation and adaptation, plants efficiently utilize resources at the leaf level, thus maximizing potential resource use for growth and reproduction. Our theory offers a robust strategy for dynamically predicting photosynthetic capacity in ESMs.
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  • Xu, Yansen, et al. (författare)
  • Mesophyll conductance limitation of photosynthesis in poplar under elevated ozone
  • 2019
  • Ingår i: Science of the Total Environment. - : Elsevier BV. - 0048-9697. ; 657, s. 136-145
  • Tidskriftsartikel (refereegranskat)abstract
    • Finite mesophyll conductance (g(m)) reduces the rate of CO2 diffusion from the leaf intercellular space to the chloroplast and constitutes a major limitation of photosynthesis in trees. While it is well established that g(m) is decreased by stressors such as drought and high temperature, few studies have investigated if the phytotoxic air pollutant ozone (O-3) affects g(m). We quantified the relative importance of three different types of limitations of photosynthesis in poplar trees exposed to elevated O-3: decreases in stomatal conductance, g(m) and biochemical photosynthetic capacity. The O-3-induced reductions in light-saturated net photosynthesis were linked to significant declines in g(m) and biochemical photosynthetic capacity (in particular carboxylation). There was no significant effect of O-3 on stomatal conductance. Of the O-3-induced limitations on photosynthesis, g(m) limitation was by far the most important (-16%) while biochemical limitation (-8%) was rather small. Both limitations grew in magnitude over the study period and varied in response to leaf-specific O-3 exposure. Our findings suggest that declines in g(m) may play a key role in limiting photosynthesis of plants exposed to elevated O-3, an effect hitherto overlooked. (C) 2018 Elsevier B.V. All rights reserved.
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  • De Kauwe, M. G., et al. (författare)
  • A test of the ‘one-point method’ for estimating maximum carboxylation capacity from field-measured, light-saturated photosynthesis
  • 2016
  • Ingår i: New Phytologist. - : Wiley. - 0028-646X .- 1469-8137. ; 210:3, s. 1130-1144
  • Tidskriftsartikel (refereegranskat)abstract
    • Simulations of photosynthesis by terrestrial biosphere models typically need a specification of the maximum carboxylation rate (Vcmax). Estimating this parameter using A–Ci curves (net photosynthesis, A, vs intercellular CO2 concentration, Ci) is laborious, which limits availability of Vcmax data. However, many multispecies field datasets include net photosynthetic rate at saturating irradiance and at ambient atmospheric CO2 concentration (Asat) measurements, from which Vcmax can be extracted using a ‘one-point method’. We used a global dataset of A–Ci curves (564 species from 46 field sites, covering a range of plant functional types) to test the validity of an alternative approach to estimate Vcmax from Asat via this ‘one-point method’. If leaf respiration during the day (Rday) is known exactly, Vcmax can be estimated with an r2 value of 0.98 and a root-mean-squared error (RMSE) of 8.19 μmol m−2 s−1. However, Rday typically must be estimated. Estimating Rday as 1.5% of Vcmax, we found that Vcmax could be estimated with an r2 of 0.95 and an RMSE of 17.1 μmol m−2 s−1. The one-point method provides a robust means to expand current databases of field-measured Vcmax, giving new potential to improve vegetation models and quantify the environmental drivers of Vcmax variation.
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  • Janhunen, P., et al. (författare)
  • Invited Article: Electric solar wind sail : Toward test missions
  • 2010
  • Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 81:11, s. 111301-
  • Tidskriftsartikel (refereegranskat)abstract
    • The electric solar wind sail (E-sail) is a space propulsion concept that uses the natural solar wind dynamic pressure for producing spacecraft thrust. In its baseline form, the E-sail consists of a number of long, thin, conducting, and centrifugally stretched tethers, which are kept in a high positive potential by an onboard electron gun. The concept gains its efficiency from the fact that the effective sail area, i.e., the potential structure of the tethers, can be millions of times larger than the physical area of the thin tethers wires, which offsets the fact that the dynamic pressure of the solar wind is very weak. Indeed, according to the most recent published estimates, an E-sail of 1 N thrust and 100 kg mass could be built in the rather near future, providing a revolutionary level of propulsive performance (specific acceleration) for travel in the solar system. Here we give a review of the ongoing technical development work of the E-sail, covering tether construction, overall mechanical design alternatives, guidance and navigation strategies, and dynamical and orbital simulations.
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